INTRODUCTION:

Coenzyme Q10 (Co-Q10) is a vitamin-like, lipid-soluble substance found naturally in cells and nutritional products. Red and white fleshes are rich in Co-Q10, and at the cellular level Co-Q10 is primarily located in the mitochondria functioning as part of electron chain transfer mechanism.^1,2

Ubiquinone is present enormously in olive oils and soybean. The daily nutritional requirement of Co-Q10 is about 5mg/kg according to many countries³.

Co-Q10 possesses antioxidant activity, acting as free radicals scavenger and minimizing oxidative damages to DNA as well as other vital intracellular lipids and proteins⁴. Ubiquinone is a cofactor for the ATP synthesis⁵ existing in two forms, ubiquinol as a reduced form and ubiquinone as oxidized pattern⁶.

Nearly 80% of Co-Q10 in healthy individuals exists in the reduced form, and is produced naturally by human body. However, by advancing in age lower levels of ubiquinone were detected especially in the presence of other age-related comorbidities. There are several proofs supporting the notion that ingestion of oral supplements of Co-Q10 would replenish the mitochondrial ubiquinone cellular deficiencies. This eventually may improve ATP synthesis and suppress the progressing of pathological age-related conditions⁷.

Oral administration of Co-Q10 was therapeutically indicated for managing different degrees of cardiac dysfunctions and to preserve vascular homeostasis in patient suffering from congestive heart failure⁸.

Additionally, nowadays Co-Q10 is widely used as an over-the-counter dietary supplement. However, the suitable and recommended daily doses of ubiquinone is yet to be specified and few if any research studies have stated its appropriate dose and bioavailability⁹.

Hazumi tanaka and colleagues reported no toxic changes in hematological parameters related to administration of Co-Q10 in a study performed on rats which were maintained on oral doses of ubiquinone for 28 days.¹⁰On the other hand, Mitsuaki Kitano and coworkers reported the formation of microgranuloma and vacuolation of hepatocytes in experiment on rats and dogs after oral administration of (300, 600, and 1200mg/kg) ubiquinone for 52 weeks.¹¹

Most recently, a daily oral dose of 300 mg/kg of Co-Q10 for 40 days was reported to predispose to selective nephrotoxicity of the podocytes.¹²

The purpose of the present study was to evaluate the safety profile of using 300mg/kg of Co Q10 oral doses on the histological structure of liver in rats.

MATERIAL AND METHODS:

Twenty Wistar rats weighing 220-270g were randomly divided into two groups: 15 treated group and 5 control group. Rats were housed in metallic wire mesh cages in the animal house of veterinary college in Tikrit University, kept at room temperature with 12 hours day/ night cycle, receiving basal dietary of water ad libitum. The guidelines of the National Committee for Research Ethics in Science and Technology were followed during animals handling and experimentation. Approval from Animal Research Ethics Committee was obtained from the University of Tikrit, College of Dentistry. The animals of the treated group received 300 mg/ kg daily dose of gelatinous capsules of Co enzyme Q10 by oral gavage for six weeks, at the end of experiment all animals were sacrificed and tissue samples of liver were excised.

The dissected liver sections of all rats were fixed in 10% neutral-buffered formaldehyde solution, then embedded in paraffin blocks. 5-μm serial sections were cut and stained with hematoxylin and eosin (H and E)^13,14. Histological observations was done for investigating of any microscopic changes using Riter light microscope.

RESULTS:

Specimens from normal control liver tissue revealed liver lobules. In the middle of each lobule is a central vein from which strands or plates of hepatocytes and sinusoids were arranged towards the periphery as shown in figure (1). Figure (2) depicts the portal triads which are formed of branches of hepatic artery, portal vein and the bile duct surrounded by connective tissue. Scattering Kupffer cells (phagocytic system) were found in the sinusoids between hepatocytes with a few vacuolated hepatocytes seen near periphery underneath connective tissue capsule as shown in figure (3).

Fig. 1: control group liver section showing plates of hepatocytes radiated from a central vein (arrow), magnification x100.

Fig. 2: control group liver section showing portal triads with few accumulated macrophages (arrow) (magnification x100)

Fig. 3: control group liver section revealing vacuolated hepatocytes underneath connective tissue capsule (magnification x100).

Specimens from the treated group exhibited an obviously abundant distribution of Kupffer cells particularly near blood vessels as seen in figure 4 (A and B). In some cases there was enlargement of Kupffer cells. Some other slides revealed aggregation of macrophages as demonstrated in figure (5).

Fig. 4: (A) Increase in distribution of Kupffer cells near blood vessels (magnification x200), (B) enlargement of Kupffer cells (arrow) (magnification x 100).

Figure (5): Aggregation of macrophages pointed by arrow (magnification x 100).

Two liver samples from the treated group showed the presence of microgranuloma as evident in figure (6). Figure (7) revealed focal necrotic (black) spots of hepatocyte. Additionally, it was observed that there was an increase in the quantity of vacuolated hepatocytes when moving or directing away from the periphery toward the depth of liver tissue compared to that of control group as shown in figure (8).

Fig. 6: Microgranuloma within hepatocytes of the Co-Q10 treated group (magnification x 100).

Fig. 7: Spotty focal necrosis (arrow) and aggregation of macrophages within hepatocytes of the Co-Q10 treated group (magnification x100).

Fig. 8: Group of vacuolated hepatocytes pointed by arrows of the Co-Q10 treated group (magnification x 100).

DISCUSSION:

In this study 15 Wistar rats were daily treated with an oral dose of 300mg/kg Co-Q10 for six weeks. Two deaths occurred in the treated group during the 4^th week of the study which might indicate the possible toxic/ near toxic dose of Co-Q10 at least to some susceptible animals. Co-Q10 is a vital mitochondrial respiratory chain repairing factor and its reduced form of ubiquinol is the only intracellular lipid-soluble antioxidants that cells can produce¹⁵. As for the histological findings, the presence of vacuolated hepatocytes which was obvious in many sections even in the deep parts of tissue away from the periphery, such observation was in consistence with several previous studies explaining those to be glycogen vacuoles¹⁶. This finding is noticed in cases of hepatic anoxia and raised intra hepatic pressure which leads to an increase in the permeability of hepatocytes and the high venous or intra hepatic pressure forces sinusoidal plasma into hepatocytes to form vacuoles¹⁷.

Although this vacuolation of hepatocytes was in agreement with other previous studies^11,18, however some researchers considered this finding of no toxicological significance^19,20.

Pertaining to the occurrence of microgranuloma in the Co-Q10 treated group, it is thought that the liver is the second organ in the frequency of involvement with granuloma after the lung and lymph nodes. Scientists define microgranuloma as 3-7 cells usually shuffled with other inflammatory cells and/or necrotic hepatocytes. This pattern although nonspecific²¹ yet it could be due to drug-induced hepatotoxicity¹¹.

Furthermore, some sections revealed spotty focal necrosis which is a term used to describe necrosis of minute clusters of hepatocytes possibly in association with lymphocytes. Necrosis involving larger groups of hepatocytes within a lobule may be referred to as focal necrosis that usually occur as a result of viral hepatitis or drug-induced liver injury²².

These changes occurring in the liver might be attributed to due to the incorporation of ubiquinol by the liver, as an adaptive response to the ingestion of an exogenous substance, while the appearance of microgranulomas and focal necrosis can be considered as the results of excessive uptake of ubiquinol, which override the ability of adaptive response, these two findings of microgranuloma and spotty necrosis are in consistence with those mentioned in a previous report¹¹.

CONCLUSION:

Based on the findings of this study it can be inferred that the ingestion of even intermediate doses of ubiquinol for long periods might lead to histopathological changes in liver such as: increase in vacuolation of hepatocytes, formation of microgranuloma which could predispose the individual to hepatic function impairment.

CONFLICT OF INTEREST:

The authors declare no conflict of interest.

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Received on 21.10.2020 Modified on 23.11.2020

Research J. Pharm. and Tech. 2021; 14(8):4025-4028.

DOI: 10.52711/0974-360X.2021.00697